48 抗蛇毒成分Cabenegrins A-IおよびA-IIの構造と合成

概要

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Two potent antidotes, cabenegrins A-I and A-II, against snake venoms have been isolated from the aqueous ethanol extract of a South American plant called "Cabeca de Negra". The structure of cabenegrin A-I(1) was fully elucidated by the NMR data. The negative CD Cotton effect at 238 nm showed the absolute configuration to be identical with that of (-)-homopterocarpin. The physical constants lead to structure 2 for cabenegrin A-II. The ^1H-NMR data showed that it is a 3:1 mixture of epimers at C-3'. The structures of cabenegrins A-I and A-II have also been confirmed by synthesis of their racemates. Cabenegrin A-I was synthesized in 11 steps starting from resorcinol. Pterocarpan ring 8 was prepared by coupling of 7 and chromen 4 in aqueous aceton in the presence of lithium chloropalladite. Introduction of side chain at C-4 was achieved by Claisen rearrangement of 10 in refluxing N,N-diethylaniline. Cleavage of double bond of 11 and the subsequent Wittig reaction on hemiacetal 13 gave E-ester 14. Reduction of 14 with LiAlH_4 in THE at -40° afforded (±)-cabenegrin A-I(1). Cabenegrin A-II was also synthesized from methyl 2,4-dihydroxy benzoate(15) in 9 steps by use of similar sequence.
天然有機化合物討論会の論文
1982-09-10